ILLUSTRATING ENGINEERING CONCEPTS WITH A
HOUSEHOLD WATER FILTER
G. Rajaram, D. M. Pai and R. S. Chauhan
Department of Mechanical Engineering
North Carolina A&T State University
1601 E Market Street, Greensboro, NC 27411
Abstract
Filtration and other methods of treatment of household drinking water supplies have become
common in order to prevent the potential health hazards that can be caused by the untreated tap
water. Filtration is been done at several stages based on the requirements from the government
body, using different types of water filters. The most common small scale water filters used in
homes use activated carbon filtration along with an ion exchange resin. In this paper, we discuss
several mechanical and materials engineering concepts that can be demonstrated using an
inexpensive household water filter pitcher. This experiment is developed for a sophomore level
engineering audience. A commercially available filter used in water pitchers is analyzed in this
experiment. The filter consists of activated carbon and ion exchange resin enclosed in a
cylindrical body. The pitcher and its filter element are used to perform flow rate calculations,
particle size measurement and pH calculations. Also, the experiment helps the student to learn
about the purification processes and the importance of activated carbon and ion exchange resins
in the field of separation and purification.
Introduction
The use of everyday life experiences serves as a great pedagogical tool for students being
exposed to engineering concepts for the first time - much like a gourmet chef’s description of the
preparation of their favorite dishes with "a little bit of this and little bit of that."1. This kind of
flexible approach helps the students to develop their critical thinking skills. Pithers and Soden2
found that college graduates are expected to learn not only the content and methods of a
discipline but also to develop 'generic' abilities. These generic abilities include a heavy emphasis
on critical thinking skills. Potential employers also place a high priority on critical thinking
skills. In a survey of industry experts and faculty, Maricle3 found that critical thinking was the
highest rated competency expected of new college graduates. We describe here a simple but
effective experiment targeted at sophomore level engineering students to engage them in critical
thinking by the use of active learning methods.
Proceedings of the 2005 American Society for Engineering Education Annual Conference & Exposition
Copyright © 2005, American Society for Engineering Education
Page 10.714.1
A commercially available pitcher-style water filter is used for this experiment. The replaceable
filter element or candle consists of activated carbon particles and ion exchange resin particles in
a cylindrical plastic container that fits into the clear body of the plastic pitcher. Carbon and resin
particles are most widely used in separation and purification purposes. The activated carbon
particles work on the adsorption principle, the trapping of impurities by strong physical bonds
within the porous structure of carbon A formal definition of adsorption4 is “The adhesion of the
molecules of gases, dissolved substances, or liquids in more or less concentrated form, to the
surface of solids or liquids with which they are in contact.”
Commercial adsorbent materials such as carbon have enormous internal surfaces. Activated
carbon has the highest volume of adsorptive porosity of any material known. Because of its large
surface area (1 quart of granules = 6 football fields5), activated carbon has a great ability to
adsorb organic molecules of liquids or vapors. Thus, when organic contaminated water is passed
through activated carbon, the contaminants are attracted and held to the internal surface walls of
the pores (Fig. 1). The contaminants get adsorbed because the attraction force of the carbon
surface is stronger than the forces that keep them in solution. Also, large volumes of gases,
including most poisonous ones, adhere to the activated carbon particles. Thus, due to its
enormous adsorption capabilities, activated carbon is popularly used in many purification
applications. Moreover, the activated carbon is very economical and easily available. Various
grains and seed husks include rice6,7, cotton-seed shell8, wheat, sunflower, flaxseed, linseed,
corn, soybean cake, jute stalk and grape marc can be pyrolyzed to a char at low temperature.
Steam activation then results in activated carbon. The carbon applications is widely used in
different industries apart from water purification like food-waste management, anti-nutrients or
toxin removal, sugar substitute purification, frying oil treatment, plant cell tissue culture media,
enzyme immobilization supports, pharmaceutical antidotes and fermentation process isolations.
Carbon particle
Pore
Impurities
Fig. 1. Activated carbon granule shown with the adsorbed impurities
Proceedings of the 2005 American Society for Engineering Education Annual Conference & Exposition
Copyright © 2005, American Society for Engineering Education
Page 10.714.2
The ion exchange process percolates water through bead-like spherical resin materials (ionexchange resins). Ions in the water are exchanged for other ions fixed to the beads. The two most
common ion-exchange methods are softening and deionization. Softening is used primarily as a
pretreatment method to reduce water hardness prior to reverse osmosis (RO) processing. The
softeners contain beads that exchange two sodium ions for every calcium or magnesium ion
removed from the "softened" water. Deionization (DI) beads exchange either hydrogen ions for
cations or hydroxyl ions for anions. The cation exchange resins, made of styrene and
divinylbenzene containing sulfonic acid groups, will exchange a hydrogen ion for any cations
they encounter (e.g., Na+, Ca++, Al+++). Similarly, the anion exchange resins, made of styrene
and containing quaternary ammonium groups, will exchange a hydroxyl ion for any anions (e.g.,
Cl-). The hydrogen ion from the cation exchanger unites with the hydroxyl ion of the anion
exchanger to form pure water. These resins may be packaged in separate bed exchangers with
separate units for the cation and anion exchange beds. Or, they may be packed in mixed bed
exchangers containing a mixture of both types of resins. In either case, the resin must be
"regenerated" once it has exchanged all its hydrogen and/or hydroxyl ions for charged
contaminants in the water. Ion exchange resins are also widely used in different applications like,
corn syrup treatment, water treatment, citrus fruit juice debittering, dye removal from waste
water, removal of organic from gases, sugar refining industry and metal recovery process.
Principle
This experiment is designed to be offered to sophomore level mechanical engineering students in
their first departmental lab course MEEN 300 – Mechanical Engineering Lab I. The experiment
is designed for the basic understanding about the
• Filtration process carried out using a pitcher water filter
• Working principle and the application of activated carbon particles and ion exchange
resin
• Flow rate calculations
• pH value measurement and its importance
• particle size measurement using a sieve scale
Experimental Procedure
Fig. 2. A household water pitcher and its filter element
Proceedings of the 2005 American Society for Engineering Education Annual Conference & Exposition
Copyright © 2005, American Society for Engineering Education
Page 10.714.3
(i)
Flow rate measurement:
Flow rate measurement is a direct measurement of water flow through the filter. Water is
poured into the filter container for purification. Different filters have different flow rates.
Also, the flow rate changes over the lifetime of the filter. In our case, we compared the flow
rates for two different brands of residential water filter pitchers. The flow rate is calculated
based on the time taken for a fixed amount of water to flow through the filter. The
experiment can be repeated for different amounts of water (in our case, 0.5 liter and 1 liter).
Sample readings are shown. The students from their own calculations learn that flow rate
depends on the starting quantity of liquid (the head) and not just on the size of the filter.
Filter A
(Using Brita Filter)
Filter B
(Using Pur Filter)
Fluid Quantity (l)
0.5
0.5
0.5
1.0
1.0
1.0
0.5
0.5
0.5
1.0
1.0
1.0
Time (s)
88
92
91
167
159
182
101
101
110
161
181
194
Flow rate (l/min)
0.341
0.326
0.330
0.359
0.377
0.330
0.297
0.297
0.273
0.373
0.332
0.310
(ii)
pH value measurement
The pH test is one of the most common analyses in water testing and a great indicator of water
quality. pH indicates the sample's acidity or alkalinity by measuring the relative amount of
hydrogen (H) and hydroxyl (OH) ions in the water. Water that has more H ions is acidic,
whereas water that has more OH ions is basic or alkaline. pH measurements runs on a scale from
0 to 14, with 7.0 considered neutral. Solutions with a pH below 7.0 are considered acids and
those between 7.0 and 14.0 are considered bases. Values from 6.8 to 7.5 are ideal for drinking
water. In our case, the pH value was measured using meter by Thermo Orion (Model 310
PerpHect LogRmeter). The unfiltered water had a pH of 7.43 (slightly alkaline) The sample data
below shows how the age of the filter element strongly affects the acidity of the filtered water,
emphasizing the need to replace filters after their useful life. This particular aspect can be studied
at length over the semester and a plot obtained of effect of number of uses of the filter on the
acidity of the filtered water.
Test #
1
2
3
Average
Filter A
6.35
6.38
6.36
6.363
Filter B
6.32
6.35
6.33
6.333
Proceedings of the 2005 American Society for Engineering Education Annual Conference & Exposition
Copyright © 2005, American Society for Engineering Education
Page 10.714.4
(iii) Particle size measurement
The carbon and the resin particles present in the filter are not of uniform size, rather the follow a
distribution. Students are exposed to the use of In order to have a general idea about the particle size
distribution present in the different filters, the filters will be cut open for particle size calculations.
There are several different ways of determining particle size. The method used in this experiment is
that of dry sieving. The sample (carbon and resin particles) is shaken mechanically through a stack
of metal sieves, of decreasing mesh size. The sediment caught in each sieve is weighed and
expressed as a percentage of the total weight of the original sample. Students are made to plot pie
charts or histograms of the particle size distribution. This is of pedagogical use as the students get
exposed to interdisciplinary concepts such as environmental engineering and catalysis.
Sieve mesh size
20
35
48
65
100
Total
Weight of particles retained (g)
14.56
50.15
4.37
0.50
0.013
69.593
% wt retained
20.92%
72.06%
6.28%
0.72%
0.02%
100
Filter A - size distribution of filter particles
0.72%
6.28%
0.02%
20.92%
Sieve Mesh
20
35
48
65
100
72.06%
Conclusions
Proceedings of the 2005 American Society for Engineering Education Annual Conference & Exposition
Copyright © 2005, American Society for Engineering Education
Page 10.714.5
The study on water filter is a simple experiment but the student gets exposed to a lot of information.
The experiment gives a basic understanding about the flow rate calculations, pH measurement and
the particle size calculations. The flow rate measurement deals with the fluid mechanics while the
pH measurement enhances the student’s basic chemistry knowledge. The particle size measurement
is a common experiment carried out by materials engineer to study the particle size distribution to
ensure the properties of the material match the requirements of the applications. Apart from the
fundamental understanding, the experiment also helps the student to understand the application of
carbon particles and the ion exchange resins in the different industry. In general, this experiment
heightens the students’ awareness of the high level of technology that go into seemingly innocuous
and low-tech kitchen gadgets and gets them to relate fundamentals learned in the classroom to their
everyday experiences.
References
1.
Scheer, S.D. (1999) “Strategies for teaching youth development in the undergraduate classroom,” College
Student Journal, 33 (1), 154-160.
2.
Pithers, R.T., & Soden, R. (2000) “Critical thinking in education: A review,” Educational Research, 42(3),
237-249.
3.
Maricle, H.K. (2003) “Entry-level competencies of animal science professionals,” Unpublished master's
thesis, University of Nebraska-Lincoln, Lincoln, NE
4.
US Dept of Energy Hydrogen, Fuel Cells and Infrastructure Technologies Program Glossary (2005),
http://www.eere.energy.gov/hydrogenandfuelcells/glossary.html
5.
Roy, G.M. (1995) “Activated carbon applications in the food and pharmaceutical industries,” Technomic
Publishing Co.
6.
Youssef, A.M., Mostafa, M.R., Dorgham, E.M. and Afinidad (1990) “Surface properties and decolorizing
power of carbons from rice husks,” Chemical Abstracts, 47(425), 41-44.
7.
Zhang, J., Zhou, H. and Huaxue Shijie (1989) “Preparation of activated carbon from carbonized rice
husk,” Chemical Abstracts, 30(7), 326-327.
8.
Zhou, X. and Huaxue Shijie (1990) “Comprehensive utilization of cottonseed shell,” Chemical Abstracts,
31(8), 375-377.
Biographies
GUKAN RAJARAM is a PhD student in the Department of Mechanical Engineering. He received the B.E. degree
in Mechanical Engineering from Madurai Kamaraj University, and his MS in Metallurgical Engineering from the
Indian Institute of Technology – Madras. His doctoral research is in the area of electrode and electrolyte synthesis
and characterization for solid oxide fuel cells. He teaches the sophomore level mechanical engineering tools lab.
DEVDAS M. PAI is a Professor of Mechanical Engineering at NC A&T State University and Associate Director
(Operations) of the Center for Advanced Materials and Smart Structures. He teaches manufacturing processes and
tribology related courses. A registered Professional Engineer in North Carolina, he serves on the Mechanical PE
Exam Committee of the National Council of Examiners for Engineers and Surveyors and is active in several
divisions of ASEE and in ASME.
RAJINDER S. CHAUHAN is an Associate Professor of Mechanical Engineering at NC A&T State University. He
has a Master of Technology in Mechanical Engineering from the Indian Institute of Technology and the Ph.D. in
Mechanical Engineering from Auburn University. He teaches courses in the energy systems stem of the mechanical
engineering program, including fluid mechanics, thermodynamics and heat transfer. He is also active in developing
and conducting lab courses in the fluids and thermal area.
Page 10.714.6
Proceedings of the 2005 American Society for Engineering Education Annual Conference & Exposition
Copyright © 2005, American Society for Engineering Education